This invention relates to a primer composition for priming a substrate surface to increase the adhesion of a sealant composition to such a surface. More particularly, this invention relates to a primer composition for priming a substrate surface which has been coated with an acid resistant coating or paint to increase the adhesion of a sealant composition to such a surface.
Urethane sealants and adhesives are known to provide high tensile and tear strengths when used to bond materials. Such sealants and adhesives are especially suitable for use in automobile manufacture for the bonding of a windshield to an automobile body, wherein the cured adhesive imparts additional structural integrity to the automobile body. However, some urethane sealants do not sufficiently bond glass to painted metal without the use of a paint primer to prepare the paint surface. Recently, the coatings industry developed acid resistant paints for use on automobiles to protect them from acidic environmental fallout such as sulfur dioxide from coal burning power plants, bird droppings, and insect fluids. The use of primers for improving the bonding of glass to painted surfaces is known and described, for example, in U.S. Pat. No. 4,525,511 which discloses a primer comprising a film-forming resin and a strong acid. U.S. Pat. No. 4,643,794 describes a primer for bonding to both glass and metal surfaces which comprises 10 to 20 parts polyester resin, 4 to 5 parts polyisocyanate cross-linking agent, 3 to 9 parts carbon black, and 66 to 83 parts volatile solvent. However, although such a primer is adapted for use on both glass and painted surfaces, it is often preferable to use different primers for priming the metal substrate and the glass which have optimum adhesion characteristics for their particular use in order to meet stringent federal motor vehicle safety standards when such a primer is used to bond windshields in automobiles. Further, it is not especially cumbersome to use multiple primer products during a glass installation process since separate applications of primer to glass and primer to paint are still necessary when a paint primer is used. The aforementioned primers were developed for use with base coat/clear coat paint systems and do not work well on newly developed acid resistant paints. Therefore, paint primers capable of adhering to acid resistant paint surfaces are desirable.